An aluminum foil has been used as a cathode collector for lithium ion batteries or electrical double-layer capacitors. Recently, since these batteries or capacitors have been diversely applied to such batteries or capacitors of electric vehicles or the like, high power and high energy density of electrode collectors in the batteries or capacitors are required. For example, an aluminum porous body having open pores with a three-dimensional mesh structure has been developed for the use of an electrode collector.
To manufacture such an aluminum porous body, for example, a foam melting method is known. In the foam melting method, molten aluminum is thickened by the addition of a thickener, and then added with titanium hydride of a foaming agent, to solidify the molten aluminum while being foamed using hydrogen gas produced through thermal decomposition reaction of titanium hydride. However, the foamed aluminum obtained by this method has a substantial amount closed pores with a size of ones of micrometers.
In another example, a method of producing foamed aluminum with a sponge backbone has been developed, and the method includes indenting aluminum in a template using sponge urethane as a core, and charging aluminum into hollow spaces formed by destruction of urethane via fire. According to this method, the foamed aluminum has open pores with a pore diameter of 40 PPI (cells per inch) or less and with a pore diameter of about 600 μm or more.
Another method of producing foamed aluminum has been developed in which foamed aluminum thereof has closed pores with a diameter of about 500 μm or less depending on the dimension of a reinforcing member. Further, the foamed aluminum thereof is produced by pressure permeating an aluminum alloy into the reinforcing member made of hollow ceramic.
In addition, a method of producing foamed aluminum has developed that includes placing a powder mixture of Al—Si alloy powder and titanium hydride (TiH2) powder in an aluminum plate and then performing hot rolling, thus foaming aluminum by decomposition of TiH2 powder. The foamed aluminum obtained by this method has a pore diameter as large as ones of micrometers.
In further examples, a method of producing foamed aluminum includes mixing aluminum with a metal having a eutectic temperature which is lower than the melting point of aluminum, and burning the mixture at a temperature greater than the eutectic temperature and lower than the melting point of aluminum. Although the foamed aluminum obtained by this method has a substantially small pore diameter, its porosity is as low as about 40%. Accordingly, the amount of cathode active material or anode active material which permeates the pores of the foamed aluminum as used as the collector is substantially low, thereby making it difficult to achieve desired high power and high energy density. The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.